There is a strong trend today, inspired by legal requirements in some areas, to employ reusable containers for soft drinks and mineral waters. This requirement is driven by both environmental and economic considerations. Soft drink bottles and other containers that have traditionally been made of glass are now increasingly being made from plastics.
Such containers may be used for a wide variety of purposes prior to their return. For example, returned containers are sometimes found to contain residues of gasoline, paint thinner or other noxious contaminants. Plastic containers are particularly prone to retaining such residues, even after washing. It is therefore very important that such contaminated containers be identified and discarded.
U.S. Pat. No. 4,830,192 to Plester et al. describes a method by which containers may be inspected for undesirable residues. The containers are partially filled with distilled water, agitated to ensure thorough mixing of any residues, and then inverted so as to pour the mixture into a cuvette for analysis. The method involves analysis carried out only in the liquid phase by a variety of physical methods, including ultraviolet (UV) visible absorption, a standard and well-known laboratory technique which has been in use for many years. The wavelengths are in the range 350-700 nm. Use of shorter UV wavelengths, of particular value in vapor phase analysis, is not described. This technique has the disadvantage of being time-consuming and requiring that each container be physically handled. Water must be added to and removed from each container, and then analyzed off-line.
For several years Photovac Incorporated of Ontario, Canada (the assignee of this application) and HNU Systems, Incorporated of Massachusetts have offered specialized products which are capable of analyzing a vapor sample, pumped from within a returned beverage container, to determine the level of organic vapor present. The analysis is performed by photoionization. The speed with which these units are able to analyze the samples is limited, however, primarily because the method of sampling requires pumping an air sample through an enclosed cell, taking a measurement, and then purging the contents. Given this limitation, multiple detectors and carousel-type container handling systems must be used in order to analyze containers moving rapidly through a production line.